mac80211: set hw initial idle state

ATM, the first call of ieee80211_do_open will configure the hw as
non-idle, even if the interface being brought up is not a monitor, and
this leads to inconsistent sequences like:

register_hw()
	do_open(sta)
		hw_config(non-idle)
(.. sta is non-idle ..)
scan(sta)
	hw_config(idle) (after scan finishes)
do_stop(sta)
do_open(sta)
(.. sta is idle ..)

Signed-off-by: Karl Beldan <karl.beldan@rivierawaves.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>